From Brighter Than a Thousand Suns, by Robert Jungk:
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Oppenheimer was convinced of Chevalier's innocence. But (Oppenheimer) gave in, and at last disclosed the name of the man whom he had himself, as he admitted later, so deeply incriminated...so saving himself and his career. Chevalier knew nothing of it, but shortly afterwards was dismissed from his tutorial post for unknown reasons. It was not until more than ten years later, after he had been driven into exile and was still without an appointment, that he finally learned who had informed against him and brought his academic career to an end.
In 1954, in an official hearing, Oppenheimer admitted that his stories about a mysterious intermediary, whom he subsequently named to Groves as Chevalier, had been "idiotic" and "a tissue of lies."
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This, from the man who was such a left-wing martyr for losing his own clearance.
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If a man lies to me the first time, what reason is there to belive he is telling the truth the second?
Rule number one: Never trust the word of a leftist. In leftist ideology a lie is an honorable and legitimate tactic to be employed in obtaining the socialist goal.